1. Field of the Invention
The present invention relates to an image forming apparatus having a storage battery.
2. Description of the Related Art
Image forming apparatuses, such as copiers, typically employ an electrophotographic method in view of high speed performance, image quality, cost, and the like, in image formation. The electrophotographic method is a method for forming a toner image on a recording medium, and fixing the formed toner image on the recording medium with heat and pressure. The heat roller method is most widely used as a fixing method for safety purposes. The heat roller method includes a mutual pressure portion, called a nip portion, at which a heating roller that applies heat by way of a heating member such as a halogen heater, is pressed to a pressing roller disposed opposite to the heating roller. The recording medium to which the toner image is transferred passes through the nip portion, and is heated and pressed, so that the toner is fixed on the recording medium.
Recently, with regard to image forming apparatuses, environmental issues have been given more importance. As a result, image forming apparatuses, such as copiers and printers, have been designed to work on energy saving. The key point of energy saving for such an image forming apparatus is power consumption of a fixing device that fixes toner on the recording medium.
To reduce the power consumption of a fixing device in a standby state where image formation is not performed, there is widely chosen a method that the temperature of the heating roller is held at a predetermined temperature that is slightly lower than a fixing temperature in the standby state, and the temperature of the heating roller is raised to the fixing temperature immediately in response to an image formation instruction. In this case, a certain amount of electric power needs to be supplied even when the fixing device is not in use, and accordingly, the image forming apparatus consumes wasteful energy. In particular, the energy consumption in the standby state is as high as about 70% to 80% of the energy consumption of components of the image forming apparatus.
Therefore, it is desirable that the energy consumption is reduced in the standby state, so that the electric power is further saved. In addition, it is desirable that no energy is supplied when the image forming apparatus is not in use. However, since the heating roller of the fixing device mainly employs a metal roller made of iron, aluminum, or the like, which has a large heat capacity, if no energy is supplied in the standby state, the fixing device needs a heating time as long as several minutes to several tens of minutes to be raised to the effective temperature (around 180° C.). This waiting time may deteriorate usability of a user, and accordingly, a heating method which has power consumption as small as possible and has a rising time from the standby state as short as possible is desired.
To reduce the temperature rising time of the heating roller, input energy per unit time, i.e., the necessary rated power can be increased. Namely, even though the temperature of the heating roller is attempted to be raised for a short period of time, the maximum input energy is determined by a power source capacity. However, the available electric power source capacity is limited in most conventional power sources, and special work is necessary for power source equipment to obtain larger electric power. Thus, it is not a common solution.
To address the problem, there has been considered an image forming apparatus that has a secondary battery which may store electric power, as an auxiliary power source. In such an image forming apparatus, the secondary battery is charged in the standby state of the fixing device, and when the fixing device is activated, electric power is supplied to the fixing device from a main power source device, and also from the secondary battery or a primary battery to reduce a rising time of the fixing device (for instance, see Japanese Patent Laid-Open No. 10-010913).
The secondary battery may be typically a lead storage battery, a nickel cadmium battery, or a nickel hydride battery. Such a secondary battery may be deteriorated in a charging capacity due to repetition of charging and discharging. In addition, the secondary battery has characteristics in that the life thereof becomes shorter as larger electric current is discharged.
When the number of rising of the temperature of the fixing device cycles increases, the repetition of the charging and discharging increases. Accordingly, the secondary battery may be degraded fast, and needs to be replaced frequently. The replacement of the secondary battery is troublesome and increases the cost of batteries to be replaced.